A 10-mmHg reduction in systolic blood pressure was associated with a significantly lower risk of all-cause mortality (risk ratio 0.87, 95% CI 0.78-0.96) and stroke events (RR 0.73, 95% CI 0.64-0.83), Kazem Rahimi, DM, of the George Institute for Global Health at the University of Oxford, and colleagues found.

The same was true for cardiovascular events (RR 0.89, 95% CI 0.83-0.95) and coronary heart disease events (RR 0.88, 95% CI 0.80-0.98), they reported in the Feb. 10 issue of the Journal of the American Medical Association.

The benefit for stroke as well as retinopathy and progression of albuminuria was found regardless of initial systolic BP, although the associations were stronger for most other outcomes when trials targeted only patients with higher baseline systolic levels (140 mmHg and higher).

When trials were stratified by achieved systolic BP, treatment was associated with lower stroke and albuminuria risks only in those that reached below 130-mmHg.

These findings argued against the controversial 2014 report from panel members appointed to what was formerly the Eighth Joint National Committee, the researchers noted.

"Thus, in contrast with the recommendations of the 2014 report for individuals at high risk of these outcomes (e.g., individuals with a history of cerebrovascular disease or individuals with mild nonproliferative diabetic retinopathy), the commencement of BP-lowering therapy below an initial systolic BP level of 140 mmHg and treatment to a systolic BP level below 130 mmHg should be considered," Rahimi and colleagues wrote.

"These findings are timely, clear, and important and lend support to current guideline recommendations to consider offering patients with type 2 diabetes antihypertensive therapy when their systolic blood pressure is 140 mmHg or greater," wrote Bryan Williams, MD, at University College London, in an accompanying editorial. "However, the findings of the study ... suggest that for some patients, these treatment thresholds and targets might be too conservative."

The authors wrote that more research on blood pressure is needed. "Further trials that evaluate BP-lowering treatment into the 120- to 130-mmHg range among hypertensive and nonhypertensive diabetic individuals would clarify whether lowering systolic BP to a target of less than 130/80 mmHg would further reduce vascular risk relative to a target of less than 140/90 mmHg," they wrote.

Williams wrote that we need a better understanding of the "genetic markers and phenotypic manifestations that predict blood pressure-mediated disease evolution in patients with diabetes.

"The information to address these important issues will not emerge from ever more aggressive treatment in older and frail patients with disease beyond the point of no return," said Williams. "To try and do so would not advance the care and improve outcomes for younger patients with diabetes."

Rahimi and colleagues looked at more than 100,000 participants in the different trials, all of which reported on outcomes for patients with diabetes who were on blood pressure lowering treatment. They included studies from 1966 to 2014, and the results of many of the studies were from diabetic subgroups in large trials with mixed populations. Follow-up in these studies, which underpinned the calculations of mortality risks, ranged from 6 months to more than 8 years; most were in the range of 2 to 5 years.

The study also looked at microvascular outcomes and found that a 10-mmHg lowering of systolic blood pressure was associated with a lower risk of retinopathy (RR 0.87, 95% CI 0.76-0.99) and albuminuria (RR 0.83, 95% CI 0.79-0.87).

Associations between lower blood pressure treatments and heart failure events and renal failure were also tested for, but these weren't found to be significant. In addition, the associations between treatment and risk of vascular outcomes were mostly not significant across classes of medication.

The authors noted that many of the trials included a relatively short follow-up time, which could mean that there wasn't enough time to observe vascular outcomes, especially for heart failure and renal failure, which are often a consequence of myocardial infarction and albuminuria.

The interpretation of the data was based on the statistical heterogeneity across subgroups and not on the results of any one trial. The authors wrote that this approach minimizes the effect of wide confidence intervals and allows for "more robust interpretation," but it also means that there's more uncertainty in the findings.

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